1. Field of the Invention
The present invention relates to a rechargeable battery.
2. Description of the Related Art
A rechargeable battery can be recharged and discharged, unlike a primary battery that cannot be recharged. A low capacity rechargeable battery has been used for a portable small electronic device such as a mobile phone, a laptop computer, and a camcorder, and a large capacity rechargeable battery has been used for a hybrid vehicle to drive a motor.
A large capacity rechargeable battery includes a plurality of unit rechargeable batteries connected in series to generate necessary power. The plurality of unit batteries are integrally coupled for stability.
Each of the unit batteries may be formed in a cylindrical shape or a rectangular shape. A rectangular unit battery typically includes an electrode assembly having a positive electrode, a separator, and a negative electrode, a case for housing the electrode assembly, and a cap plate for closing and sealing the case.
The cap plate includes a terminal hole protruding externally from the cap plate, an electrode terminal electrically connected to the electrode assembly, an electrolyte injection opening formed to allow electrolyte solution to be injected into the case, the electrolyte injection opening being sealed with a sealing cap, and a discharge hole formed to discharge gas generated inside the case, the discharge hole closed and sealed with a vent plate.
The electrolyte injection opening enables injecting of the electrolyte solution after inserting the electrode assembly in the case and closing and sealing the case with the cap plate. The electrolyte injection opening is closed and sealed with the sealing cap through welding after injecting the electrolyte solution.
The electrolyte injection opening and the sealing cap are formed in a two-stage structure, such as with a cylindrical shape and a circular shape, respectively. Since the electrolyte injection opening and the sealing cap are respectively formed in the cylindrical shape and the circular shape, a wide interference area may be formed between the electrolyte injection opening and the sealing cap. Accordingly, the wide interference area makes designing an allowable tolerance difficult.
Since the electrolyte injection opening and the sealing cap are formed in the two-stage structure, such as a cylindrical shape and a circular shape, centers of the two stages of the electrolyte injection opening may not be aligned with centers of the two stages of the sealing cap. In this case, it is difficult to insert the sealing cap into the electrolyte injection opening, and productivity is deteriorated.
During a welding process, a pre-welding process is required to weld the sealing cap to the electrolyte injection opening in order to fix the sealing cap and prevent thermal distortion. Therefore, productivity is deteriorated. Welding quality is also deteriorated if the sealing cap is not smoothly fixed.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.